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SOME DATA RELATING TO TYPICAL BRITISH AERO ENGINES IN 1919 (From Lord Weir, of Eastwood)

521

Description of Engine

Bore in

inches

Stroke in inches

Com- pres- sion ratio

Piston speed in ft. per min.

B.H.P.

Revs, per minute

Mean eff. Press. Lb./d.

Weight in Ib.

Lb. per normal H.P. hour

Nor- mal

Max.

Norm, of engine

Norm, of pro- peller

Maxm. of

engine

Total (dry)

Per H.P.

dry

Per H.P. wet

Norm.

Max.

of Petrol

of Oil

Rotary g-cyl. air- cooled Bentley

5-52

7-08

5-26

1536

230

234

1300

1300

1360

92-0

_

498

2-165

630

088

Radial 9-cyl. air- cooled A.B.C. " Dragon Fly "

5'5

6-5

4-42

1787

320

350

1650

1650

1750

IIO-O

635

1-980

585

028

Vertical 6-cyl. water - .cooled Siddeley

" Puma "

5-72

7-48

5-oo

1745

250

266

14.00

1400

1500

115-0

123

645

2-58

600

062

Diagonal, 2 rows of 4 cyls. at 90, water- cooled Sun- beam " Arab "

4-73

5-12

5-3

1707

212

220

2000

1 200

2IOO

II2-0

550

2-60

3-24

486

039

Diagonal, 2 rows of 6 cyls. at 60, water- cooled Rolls- Royce " Eagle VIII." ..

4-5

6-5

5-3

1950

359

368

1800

1080

iqoo

127-2

I3I-4 at 1500

926

2-58

3-23

500

025

Diagonal, 2 rows of 6 cyls. at 60, water- cooled Gallo- way " A t- lantic ".

5-72 *

7-48

5-40

1872

550

575

1500

1500

1600

126-3

1150

2-09

2-74

504

045

Diagonal, 2 rows of 6 cyls. at 60, water- cooled Rolls- Royce " Con- dor "

5-5

7'5

5-io

%

2187

610

656

1750

222

2OOO

129-0

129-4

1350

2-21

2-86

495

023

Diagonal, 3 rows of 4 cyls. at 60, water- cooled Napier " Lion ".

5-5

5-125

5-35

1708

450

468

200O

840

2200

I22-O

126-0

1318

1-86

2-51

495

023

engines in 1910 by Burls 1 showed that 10 were horizontal, 12 radial, 25 diagonal, 24 vertical or " straight " and 5 rotary. With few exceptions the horizontal, diagonal, and vertical engines were water-cooled, the radial mostly air-cooled, and the rotary all air-cooled. Horse-power ranged from 15 to 130, but in aeroplane service from 60 to 120 was usually found. The weight per B.H.P. even in 1910 ranged from slightly under 2 Ib. in the " Gnome " type of engine, illustrated in fig. 15, to as much as 7 Ib. in water-cooled types in the remaining classes.

In July 1919, Lord Weir of Eastwood 2 gave a table (see above) of data relating to current typical British aero engines; it will be seen that vertical, rotary, radial and diagonal designs are all represented, the last-named predominating. The largely increased power of the 1919 engines is noteworthy; in 1910 the practical maximum used was about 130; in Lord Weir's table the maxi- mum is 610 B.H.P. The 1919 engines show also a very satis- factorily low consumption of petrol and lubricating oil.

Considerable reduction has also been effected in the weight per B.H.P. of the water-cooled diagonal-type engines, which range from 3j Ib. down to only 2! Ib. In the engines of 1910 the average piston speed was, roundly, 1,100 ft. per minute; the average of the eight engines in the above table is roundly 1,800 ft. per minute, a substantial and noteworthy increase.

The power of aero engines is usually stated at ground level ; with increase of altitude the power output diminishes owing to the lessened density of the air; if at ground level a full power of 100 H.P. be obtained, at 5,000 ft. elevation this falls to about 82, and at 10,000 ft. to only about 68. To provide for this loss some aircraft engines have been designed for partly throttled running only at ground level, full throttle being only used when working in rarefied air at a suit- able altitude; in these engines large compression ratio and forced induction are usually adopted, and full power output is never at-

1 "Aero Engines," G. A. Burls (Charles Griffin).


 * Proc. of N.E. Coast Inst. of Engineers and Shipbuilders.

tempted at the ground level. In other cases a blower is provided to deliver additional air to the cylinders at high altitudes; exhaust- driven turbines of high efficiency have been developed by Rateau for this supercharging; by this means a nearly constant pressure may be maintained in the cylinders at the end of the suction stroke, with consequent constant power output at all heights.

In radial, as in rotary, engines a star- wise arrangement of the cylinders is adopted, all the pistons operating upon one or two cranks only, but the cylinders are stationary and the crankshaft rotates. Designs have appeared including 3, 5, 7, 9, 10 and 14 cylinders, the two last in two planes.

The 9-cylindered air-cooled radial engine of the Cosmos Co. developed 450 H.P. with the extremely low weight of but 1-47 Ib. per horse-power; but large radial engines are open to objection on account of the increased head resistance involved in their use. With vertical or " straight " engines, i.e. those in which the cylinders are arranged as in the normal motor-car engine, weight per horse- power is found to diminish up to about four cylinders; thereafter, the larger crankshaft and heavier crank-case necessary to provide adequate stiffness tend to cause the weight per horse-power to in- crease; designers have accordingly associated cylinders together in two or more rows, and the " diagonal " engine with two or more pistons operating on each crank-pin is thus frequently met with in recent high-powered engines.

Weight is also saved and mechanical efficiency increased by operating the valves directly from overhead cam-shafts. Aluminium alloys are also largely used for pistons and cylinders, the latter being fitted with thin steel or cast-iron working barrels.

In their 45O-H.P. engine Messrs. Napier have three rows each of four cylinders, twelve in all, three connecting-rods being attached to each crank-pin; the weight is thus reduced to only 2\ Ib. per B.H.P. " wet."

The latest design of this form in 1921 was a sixteen-cylindered l,ooo-H.P. aero engine, illustrated in external view in fig. 16 (Plate). In this engine there are four rows or " banks," each of four cylinders; the cylinders are separate, each being machined from a solid steel forging, with water-jackets formed of light steel pressings welded on.

The vertical angle between the axes of the cylinder rows is 52^, side angle 90, and angle at base 1275"; the engine may be regarded as formed of two eight-cylinder 90 diagonal engines placed back-to- back, and jointly actuating a " flat four-throw " crank-shaft, with